1. Field of the Invention
The present invention relates to medical devices for percutaneously accessing body lumens and, more particularly, to methods and devices for accessing the cardiovascular system.
2. Description of the Related Art
A wide variety of diagnostic or therapeutic procedures involve the introduction of a device into the vasculature through a percutaneous or open surgical incision at an access site. Such regions of the vasculature, preferred for access, include both the iliac, subclavian, and femoral arteries. A percutaneous technique commonly known for such vascular access is the Seldinger technique. The Seldinger technique involves using a hollow needle to puncture the skin and gain access to the selected artery or vein. A guidewire is next placed through the hollow needle into the selected region of vasculature. The guidewire may be advanced to a target location in the vasculature, which can be more than 100 cm away from the access site. The needle is removed and a tapered dilator with a sheath and a central lumen in the dilator is advanced over the guidewire into the vasculature. The dilator is next removed and a guide catheter is advanced through the sheath over the guidewire. The guide catheter can be advanced all the way, or part way, to the target site. The guide catheter, following, or without, removal of the guidewire can be used for directing therapeutic or diagnostic catheters to regions of the vasculature and central circulation, including external and internal structures of the heart. A general objective of access systems, which have been developed for this purpose, is to minimize the cross-sectional area of the access lumen, while maximizing the available space for the diagnostic or therapeutic catheter placement therethrough. These procedures are especially suited for coronary angioplasty, stent placement, cardiac valve replacement, stent-graft placement, cerebrovascular embolic coil placement, diagnostic cardiac catheterization, cardiac assist, and the like.
One type of cardiac procedure involves placement of a collapsible cardiac valve in either the aortic, tricuspid, or mitral position. Today, an aortic valve replacement procedure involves the steps of inserting a hollow needle, with a hemostasis valve affixed to its proximal end, into the femoral or iliac artery of a patient via a percutaneous puncture. A guidewire is next inserted through the hemostasis valve and the central lumen of the needle into the femoral or iliac artery. The guidewire is routed, under fluoroscopic control, cranially toward the heart, through the aortic arch, through the aortic valve and into the left ventricle. The hollow needle is removed from the patient leaving the guidewire in place. An introduction sheath, including a tapered tip central obturator or dilator having a hemostasis valve at its proximal end and further including a central guidewire lumen is routed over the guidewire, through the skin puncture, through the wall of the artery, and into the central lumen of the iliac artery or aorta. The central obturator or dilator is removed. A valve delivery catheter is next advanced over the guidewire and through the introduction sheath to the region of the aortic root. The aortic valve is deployed in the region of the aortic root such that the remnants of the original valve are outwardly dilated by the implant, which comprises a valve and expandable support stent. The valve is seated firmly so as to become secured to the aortic valve remnant. The delivery catheter is next removed from the patient leaving the new valve in place. The sheath is next removed and hemostasis is established using standard techniques for a vessel puncture wound. Indications for percutaneous valve replacement include a stenotic or incompetent aortic valve and a contraindication to open surgical valve replacement.
Issues can arise, however, when the delivery catheter or sheath are removed from the patient. Withdrawal of large catheters and sheaths has been reported to cause disruption of vessel plaque during removal or pullback through the aorta, iliac and femoral arteries. This is especially problematic in very sick patients with significant vascular disease that involves plaque, mural thrombus, aneurysms, and other pathologies. The disruption of a region of plaque or thrombus can cause emboli to break free from the vessel wall, float downstream, and lodge within the lumen of smaller distal vessels, blocking blood flow, and resulting in ischemia and possibly tissue necrosis. Not only during withdrawal, but also during insertion, do issues arise with insertion of sheaths and catheters. In patients suffering form substantial cardiovascular disease, atheroma, thrombus, and other plaque can build up on the interior of the abdominal aorta, iliac arteries, and femoral arteries. These vessels can have their lumen diameters substantially reduced by these buildups and furthermore, the vessels can become highly tortuous. Thus, insertion of catheters, especially large diameter catheters and introducer sheaths can be difficult or impossible because of vessel stenosis or wall interference.
Suggested further reading related to the use of iliac or femoral introducers for large catheters includes Gawenda M, and Brunkwall J, Device-Related Problems of Thoracic Stent-Grafts, 1: Zentralbl Chir. 2007 June; 132(3):205-10, the entirety of which is hereby incorporated by reference herein.
It is desirable to protect the arteries, including the femoral and iliac arteries, from a delivery catheter and sheath during removal. A need remains, therefore, for improved access technology, which allows a large diameter catheter or sheath to be percutaneously or surgically introduced through the iliac, femoral, or subclavian arteries, and then be removed without causing further injury or complications to the patient.